1. Field of the Invention
The present invention relates to a technology for performing microstep driving of a stepping motor used for, for example, feeding the pickup of an optical-disk playback apparatus.
2. Description of the Related Art
Conventionally, a technology for performing microstep driving of a stepping motor used for feeding the pickup of an optical-disk playback apparatus is known (e.g., Japanese Unexamined Patent Application Publication No. 2001-76448). The microstep driving is a driving method for controlling the stepping motor by using, as units, angles obtained by dividing a basic step angle of the stepping motor into multiple angles. Herein, for convenience, the number of angles obtained by dividing the basic step angle is referred to as a “microstep division number” and the angle obtained by dividing the basic step angle by the microstep division number is referred to as a “microstep angle”.
Another technology for driving a stepping motor used for feeding the pickup of the optical-disk playback apparatus is known (e.g., Japanese Unexamined Patent Application Publication No. 2004-139656). In this technology, when the value of a drive signal is changed so that the rotation angle of the stepping motor advances by one step angle and the stepping motor does not rotate in response to the change, the value of the drive signal is gradually increased.
For the microstep driving of a stepping motor used for feeding the pickup of an optical-disk playback apparatus, as the microstep division number is increased, the amount of change in a drive signal for changing the rotation angle of the stepping motor by one microstep angle decreases and the change reduces the impact on the rotor of the stepping motor. This makes it difficult to cause the rotation of the rotor of the stepping motor by overcoming the load at the point, even when the value of the drive signal is changed so that the rotation angle of the stepping motor changes by one microstep angle. As a result, a response of the rotation angle of the stepping motor relative to a change in the value of the drive signal deteriorates.
In such a case, when the technology disclosed in Japanese Unexamined Patent Application Publication No. 2004-139656 described above is used to gradually change the value of the drive signal by a predetermined value until the stepping motor rotates, there is a problem. That is, since the impact that a change in the value of the driving signal has on the rotor of the stepping motor at each time is equal, the value of the drive signal needs to be changed by the predetermined value multiple times until the stepping motor rotates, when the impact is not sufficiently strong to start the rotation of the rotor of the stepping motor. As a result, a large amount of time is required until the rotor of the stepping motor rotates and the value of the driving signal increases cumulatively. Thus, during the rotation of the stepping motor, the amount of change in the rotation angle of the stepping motor may become significantly larger than a desired change in the rotation angle. On the other hand, when the predetermined value is sufficiently increased, the stepping motor can be quickly rotated. With this arrangement, however, during the rotation of the stepping motor, the amount of difference between a change in the rotation angle of the stepping motor and a desired change in the rotation angle always becomes large.
Therefore, according to the known technologies, it is difficult to perform servo control of the stepping motor with sufficient accuracy when the microstep division number is increased.